的一個(gè)重點(diǎn)在於下層的協(xié)定提供服務(wù)給其上一層課件

1、Transport Layer2022/9/251Transport Layer2022/9/241OutlineFunctions of Transport LayerTransport Layer Protocols that are in useTCPUDP2022/9/252OutlineFunctions of Transport Transport layer2022/9/253Transport layer2022/9/243Transport layerTransport layer servicing its upper layerTransport layer reliev

2、ing its lower layers burden2022/9/254Transport layerTransport layerLayered protocols 的一個(gè)重點(diǎn)在於下層的協(xié)定提供服務(wù)給其上一層1. 那 思考一下，Application Layer 有 哪些應(yīng)用？2. 你覺(jué)得 Transport 需哪些功能以提供這 些應(yīng)用所需？2022/9/255Layered protocols 的一個(gè)重點(diǎn)在於下層的協(xié)定Application Layer 有哪些應(yīng)用？2022/9/256Application Layer 有哪些應(yīng)用？2022/9Facts learned from pre

3、vious slide 有很多應(yīng)用，同時(shí)經(jīng)由網(wǎng)路與遠(yuǎn)端另一主機(jī)溝通Can you name a few of these applications?MSN, IE, etc每種應(yīng)用的特性不同Can you name a few of these characteristics?Email vs Internet phone (Skype)2022/9/257Facts learned from previous slFirst problem:很多應(yīng)用，同時(shí)經(jīng)由網(wǎng)路與遠(yuǎn)端另一主機(jī)溝通 2022/9/258First problem:很多應(yīng)用，同時(shí)經(jīng)由網(wǎng)路與遠(yuǎn)端很多應(yīng)用，同時(shí)經(jīng)由網(wǎng)路與遠(yuǎn)端另一主

4、機(jī)溝通 Can we transport a full chunk of large application data at one time?If not, what would you do? accepts data from different conversations and segments/passes it down to the lower layers as manageable pieces that can be eventually multiplexed over the media.2022/9/259很多應(yīng)用，同時(shí)經(jīng)由網(wǎng)路與遠(yuǎn)端另一主機(jī)溝通 Can we tT

5、ransports primary responsibilitiesSegmenting data and managing each pieceIdentifying & Tracking individual communication between applications on the source and destination hostsReassembling the segments (seq. #)into streams of application data2022/9/2510Transports primary responsibiSegmentation2022/

6、9/2511Segmentation2022/9/2411SegmentationDividing data into small parts, and sending these parts from the source to the destination, enables many different communications to be interleaved (multiplexed) on the same network. So that you could receive e-mails, chat on instant messenger, view web pages

7、 or video at the same time.2022/9/2512SegmentationDividing data intoTracking multiple streamsVarious applications running concurrently2022/9/2513Tracking multiple streamsVarioIdentifying the Applications(with port number)2022/9/2514Identifying the Applications(Re-assembling segments(with sequence nu

8、mber)2022/9/2515Re-assembling segments(with s實(shí)例：TCP & UDP HeadersWhat are these fields related toThe above mentioned functions?2022/9/2516實(shí)例：TCP & UDP HeadersWhat are tSecond problem:每種應(yīng)用的特性不同2022/9/2517Second problem:每種應(yīng)用的特性不同2022Data Requirements VaryDifferent applications have different requireme

9、nts, there are multiple Transport layer protocols. For some applications, segments must arrive in a very specific sequence in order to be processed successfully. In some cases, all of the data must be received for any of it to be of use. In other cases, an application can tolerate some loss of data

10、during transmission over the network. 2022/9/2518Data Requirements VaryDifferenConsequently The different Transport layer protocols have different rules allowing devices to handle these diverse data requirementsIn todays converged networks, applications with very different transport needs may be com

11、municating on the same network.2022/9/2519Consequently The different TrExample - 1An e-mail or web page need to be completely received and presented for the information to be considered useful. Slight delays are considered acceptable to ensure that the complete information is received and presented.

12、2022/9/2520Example - 1An e-mail or web paExample - 2Occasionally missing small parts of a telephone conversation might be considered acceptable. One can either infer the missing audio from the context of the conversationor ask the other person to repeat what they said. This is considered preferable

13、to the delays that would result from asking the network to manage and resend missing segments. In this example, the user - not the network - manages the resending or replacement of missing information.2022/9/2521Example - 2Occasionally missinTransport layers functions may also need to include If req

14、uired, ensures that all the data is received reliably and in order by the correct applicationEmploys error handling mechanisms2022/9/2522Transport layers functions maThe primary functions all Transport layer protocols should supportSegmentation and ReassemblyConversation MultiplexingAt the Transport

15、 layer, each particular set of pieces flowing between a source application and a destination application is known as a conversation Both TCP and UDP support these two functions 2022/9/2523The primary functions all TranSome Transport layer protocol may need more Connection-oriented conversationsRelia

16、ble deliveryOrdered data reconstructionFlow control Only TCP support these functions 2022/9/2524Some Transport layer protocol Thats why there are TCP : Transport Control ProtocolandUDP : User Datagram Protocol2022/9/2525Thats why there are TCP : TrTCP & UDP Headers - againWhat are these two differen

17、t protocolrelated to the above mentioned functions?2022/9/2526TCP & UDP Headers - againWhat How can Transport layer Establish a connection-oriented connection?Ensure reliable delivery?Maintain same order delivery?Execute flow control? Later when we talk about TCP2022/9/2527How can Transport layer Es

18、tabWhen do we need reliability?It depends on the applicationsApplications developer choose the appropriate transport layer protocol based on the nature of the application2022/9/2528When do we need reliability?ItDifferent applications require different transport layer support2022/9/2529Different appl

19、ications requireApplications that need reliabilityDatabases, web pages, and e-mail, require all of the sent data arrive at the destination in its original condition, in order for the data to be useful. Any missing data could cause a corrupt communication that is either incomplete or unreadable. The

20、additional network overhead (as a result of ensuring reliability) is considered to be required for these applications.Use TCP2022/9/2530Applications that need reliabiApplications that do not need reliabilityAudio & Video streamFor example, if one or two segments of a video stream fail to arrive, it

21、would only create a momentary disruption in the stream. This may appear as distortion in the image but may not even be noticeable to the user. Use UDP2022/9/2531Applications that do not need TCP in detailsThe key distinction between TCP and UDP is reliability2022/9/2532TCP in detailsThe key distinct

22、How does TCP ensure reliability?Sequence number in each segmentPositively acknowledge to the sender upon receiving segmentsRetransmit segments if no acknowledge is received from the receiver2022/9/2533How does TCP ensure reliabilitSequence number & Ack number2022/9/2534Sequence number & Ack number20

23、Positive Acknowledgement2022/9/2535Positive Acknowledgement2022/9TCP Retransmission2022/9/2536TCP Retransmission2022/9/2436FlagsURG - Urgent pointer field ACK - Acknowledgement field PSH - Push functionRST - Reset the connectionSYN - Synchronize sequence numbersFIN - No more data from sender2022/9/2

24、537FlagsURG - Urgent pointer fielTCP connection establishmentestablishing connection-oriented connection(three-way handshake)2022/9/2538TCP connection establishmenteDetails on 3-way handshake - 12022/9/2539Details on 3-way handshake - 1Details on 3-way handshake - 22022/9/2540Details on 3-way handsh

25、ake - 2Details on 3-way handshake - 32022/9/2541Details on 3-way handshake - 3Simple Acknowledgement2022/9/2542Simple Acknowledgement2022/9/2Whats the problem with SimpleAcknowledgement?Network usage efficiency2022/9/2543Whats the problem with SimpleAdjust the Window Size (=3)2022/9/2544Adjust the W

26、indow Size (=3)202Window Size TCPs wayWindow size determines the amount of data that can be transmitted at one time before receiving an acknowledgementAfter a host transmits the window-sized number of bytes, it must receive an acknowledgement before it can send any more messages2022/9/2545Window Siz

27、e TCPs wayWindow Window Size TCPs way2022/9/2546Window Size TCPs way2022/9/Window Size TCPs way2022/9/2547Window Size TCPs way2022/9/Sliding WindowsWindow Size is changingTo achieve FLOW CONTROLSend more packets when remote buffer can accommodate, send less packets when remote buffer is almost fullI

28、t is just like SLIDE the window to allow more or less air in2022/9/2548Sliding WindowsWindow Size is TCP connection termination2022/9/2549TCP connection termination2022TCP Termination - FIN2022/9/2550TCP Termination - FIN2022/9/24TCP Termination - ACK2022/9/2551TCP Termination - ACK2022/9/24TCP Term

29、ination - FIN2022/9/2552TCP Termination - FIN2022/9/24FIN vs RSTA graceful end by sending a FIN packet followed by a received ACK FIN packet. A not-so-graceful end when one part just hangs-up. In this case TCP sends a RST (reset) packet closing the connection. 2022/9/2553FIN vs RSTA graceful end by

30、seRe-assembling segments(with sequence number)2022/9/2554Re-assembling segments(with sRe-assembling segmentsDuring session setup, an initial sequence number (ISN) is set 3-Way HandshakeThis ISN represents the starting value for the bytes for this session that will be transmitted to the receiving app

31、lication. As data is transmitted during the session, the sequence number is incremented by the number of bytes that have been transmitted. This tracking of data byte enables each segment to be uniquely identified and acknowledged. Missing segments can be identified. 2022/9/2555Re-assembling segmentsDuring sHow to re-assembly & maintain